The present invention concerns a cam follower in a valve train of an internal combustion engine switchable between different lifts for at least one gas-exchange valve and having the following characteristics:
a) the cam follower includes at least two adjoining sections acted upon by cams with different lift, one of these sections alternatively not cooperating with a cam; PA1 b) the sections possess cavities preferably aligned with each other in a cam base-circle phase, movable coupling means in at least one of the cavities, the means being positioned in the decoupled state of the sections completely in their cavity; PA1 c) the coupling means can be shifted in the coupling direction via hydraulic fluid which can be delivered via an inlet to a pressure chamber formed by their cavity axially in front of their end wall on the pressure-chamber side, the means being shiftable across a separating surface between the sections for coupling of the sections such that part of the means engages in the adjoining cavity; PA1 d) the coupling means communicate with locking or shut-off means.
A cam follower of this type with locking means is known from DE-OS 196 22 174. According to FIG. 8, for example, its locking means have the form of a ball which is designed to engage in positive fashion into the piston-shaped coupling means. Here, the ball extends beyond a cavity for the coupling means in the direction of the cam shaft. An engaging cam, in turn, possesses on its outer wall a partially recessed annular groove which cooperates with the ball for locking purposes.
A disadvantage of this type of cam follower is the fact that the locking means require complicated changes to already existing cams of cam shafts. At the same time, unnecessarily high wear occurs in this region of the locking means through the cam contact. If hydraulic fluid is introduced ahead of the coupling means possessing the locking means, one also has to reckon with an additional loss of hydraulic fluid via the recess in the cam follower for the locking means. One likewise finds that the measures undertaken on the mentioned cam follower for locking its coupling means outside the desired cam-contact phases themselves necessitate complicated changes in the cam follower. At the same time, the stiffness of the locking means can lead in rare cases to undesired loading or destruction of structural parts.